The present invention relates to a wet paper web transfer belt used in a papermaking machine.
Papermaking machines for removing moisture from the source material of paper are generally equipped with a wire part, a press part and a dryer part. These parts are arranged in the order of wire part, press part and dryer part in the wet paper web transfer direction.
Regarding passing of a wet paper web in the press part, there is currently known, as a papermaking machine, a closed-draw papermaking machine in which the wet paper web is passed in closed-draw. In the press part of the closed-draw papermaking machine, the wet paper web is transferred while being placed on a papermaking felt or a wet paper web transfer belt, and therefore there is no part in which the wet paper web travels on its own and occurrence of web breaks is prevented. Thus, the closed-draw papermaking machine has an excellent aptitude for high-speed operation and excellent operation stability.
One example of a press part of a typical closed-draw papermaking machine will be described by referring to FIG. 5. In FIG. 5, a wet paper web WW shown by a broken line is supported by a wire WF of a wire part, press felts PF1, PF2, and PF3 of a press part, a wet paper web transfer belt TB, and a dryer fabric DF of a dryer part and is transferred from left to right. As described above, there is no part in which the wet paper web is not supported in the closed-draw papermaking machine. As is well known, the wire WF, the press felts PF1, PF2, and PF3, the wet paper web transfer belt TB, and the dryer fabric DF are endless band-shaped bodies and are supported by guide rollers GR.
Note that, in FIG. 5, press rolls PR1, PR2, and PR3, a shoe PS, a shoe press belt SB, and a suction roll SR are all well-known structures. The press rolls PR1 and PR2 constitute a first press portion PP1, and the concave shoe PS corresponding to the press roll PR3 and the press roll PR3 constitute a second press portion PP2 via the shoe press belt SB.
Herein, a traveling state of the wet paper web WW in the closed-draw papermaking machine will be described. Note that, as a matter of course, the wet paper web WW has a continuous shape, and therefore the traveling state of a part of the wet paper web WW will be described.
First, the wet paper web WW passes through the wire WF of the wire part, the press felt 1 of the press part, and the first press portion PP1 in turn and is passed via the press felt PF2 to the press felt PF3. Then, the wet paper web WW is transferred by the press felt PF2 to the second press portion PP2. In the second press portion PP2, the wet paper web WW is pressed by the shoe PS via the shoe press belt SB and the press roll PR3 while being sandwiched between the press felt PF3 and the wet paper web transfer belt TB.
In this case, the press felt PF3 is configured to have high water permeability, and the wet paper web transfer belt TB is configured to have remarkably low water permeability. Therefore, in the second press section PP2, moisture from the wet paper web WW moves to the press felt PF3.
Immediately after exiting from the second press section PP2, the press felt PF3, the wet paper web WW, and the wet paper web transfer belt TB are suddenly released from pressure and therefore swell in volume. Due to this swelling and a capillary action of pulp fibers constituting the wet paper web WW, a so-called “rewetting phenomenon” in which part of the moisture in the press felt PF3 moves to the wet paper web WW occurs.
As described above, however, the wet paper web transfer belt TB is configured to have remarkably low water permeability, and therefore no moisture is held on the inside thereof. Therefore, the rewetting phenomenon hardly occurs from the wet paper web transfer belt TB, and the wet paper web transfer belt TB contributes to improving water squeezing efficiency of the wet paper web. Note that the wet paper web WW that has exited from the second press portion PP2 is transferred by the wet paper web transfer belt TB. Then, the wet paper web WW is attached to the suction roll SR and is transferred by the dryer fabric DF to the dryer part.
Herein, the wet paper web transfer belt TB is demanded to have a function (wet paper web adhesive property) of transferring the wet paper web WW while causing the wet paper web WW to adhere to a wet paper web carrying surface (outer circumferential surface) of a wet paper web carrying side resin layer after the wet paper web transfer belt TB exits from the second press portion PP2 and a function (wet paper web release property) of smoothly releasing the wet paper web when the wet paper web WW is passed to the next part and is also demanded to have a function (antifouling property) of preventing contamination components (sizing agents, fillers, reactants thereof, and the like) contained in the wet paper web from adhering to or being accumulated on the wet paper web carrying surface.
Further, the wet paper web transfer belt TB is supported by a plurality of guide rollers GR and the press roll PR3 and therefore is particularly demanded to have wear resistance on a roll contacting surface (inner circumferential surface) of a roll side resin layer.
Some studies regarding the wet paper web transfer belt have been made for improving the wet paper web adhesive property and the wet paper web release property of the wet paper web carrying surface, i.e., wet paper web transfer properties thereof and improving the wear resistance of the roll side resin layer (for example, JP H6-57678A, JP 2014-62337A, JP 2014-62338A, EP patent application publication No. 1069235, specification, and JP 2009-127134A). JP H6-57678A, JP 2014-62337A, and JP 2014-62338A disclose a belt in which the wet paper web transfer properties are improved by setting surface roughness Ra or Rz of the belt within a predetermined range. EP patent application publication No. 1069235, specification discloses a belt in which the wet paper web transfer properties are improved by causing an outer layer of the belt to be porous.
JP 2009-127134A discloses a belt in which the wear resistance of a roll side layer is improved by providing the roll side layer made of batt fibers containing low melting point nylon and melting a roll contacting surface of the roll side layer to form a welded layer.